I tried changing capture scrolling delay, but no change. It will work in certain other app & things like Explorer windows. Even then, doesn't seem to capture screen part that is wider than the monitor.

Unfortunately the feature of a screen capture of a scrolling window doesn't works completely. Surely is the developers of PicPick this problem known. But probably a complete solution is too complicated. I have tested the feature in different cases on a PC, where Windows XP SP3 is installed. Here are my results:

Feature works

Mozilla Firefox, Portable Edition v18.0.1

Google Chrome Portable v24.0.1312.56

Internet Explorer v8

Adobe Reader v10.1.5

Windows Explorer

Microsoft Office Excel 2007 (but I must stop the capturing with the key "Esc" on my keyboard)

Perhaps the combination of Vista & Firefox create problems for many capture prgms scrolling capture. I don't think there'd be any difference in portable Fx & installed. But, you're using XP. I remember FastStone Capture's scrolling capture quit when I switched from XP to Vista, though all other features still worked. But many that can't scrolling capture in Fx, can in IE. I just never use IE.

In Firefox, Screenshot Captor - as a stand alone - works for scrolling captures.
Fireshot addon worked - when last tried it a few Fx ver ago. I'd just have to enable it & restart when I want to use it, as I've got enough other important addons running constantly.